1. Field of the Invention
The present invention is directed toward a viscometer which permits determination of viscosity of an expanding foam material on the basis of axial pressure measurements and foam rise measurements and, more specifically, relates to such a system which employs motionless apparatus.
2. Description of the Prior Art
In recent years, numerous commercial uses have been made of polymeric foam materials. Among the numerous uses are, for example, uses in residential and commercial building products as thermal insulation, as well as other thermal insulation uses, as in refrigerators, and uses in automotive and household seating and bedding materials.
It has been known to use flexible, as well as foamed polyurethane, and phenolics, as well as other polymeric foams which are produced by casting in a mold.
Among the problems encountered in connection with such uses have been cell structure defects, excessive curvature or other deformations, undesired mold leakage, and undesired changes in density. In the past, efforts to obtain reliable information as to the molding properties of specific foamed synthetic resin precursor systems of a small-scale basis and extrapolating the results to large scale, have been generally unsuccessful. As a result, expensive, large-scale testing has been required.
Various means have been suggested for determining viscosities for plastics, in general, as distinguished from foamed plastics. U.S. Pat. No. 3,138,950 disclosed measurement of polymer melt viscosities through use of strain gauges. See also, U.S. Pat. No. 3,559,464 which discloses monitoring of a plastic in a Rheometer which employs two distinct capillaries of different length and associated pressure gauges in cooperation with a computer.
U.S. Pat. No. 3,194,057 disclosed a viscometer which employs ultrasonic waves and attenuation thereof as a means for measuring viscosity of fluids.
U.S. Pat. No. 3,360,986 relates to foaming plastics and a system wherein a predetermined volume chamber receives the plastics at a pressure which prevents foaming. A ram urges the plastic through the capillary and the time required for a particular quantity of the plastic to be extruded is recorded with the shear rate being determined.
U.S. Pat. No. 4,137,754 relates to a melt rheometer for measurement of flow properties of foamable plastics. The material is introduced into an extruder and mixed with a blowing agent which is introduced through a port. Movement of the piston coordinates feed of the blowing agent. The material is forced through a capillary orifice. Pressure transducers are employed.
A study of the basic heat balance of a foaming polyurethane system is disclosed in Campbell "Polyurethane Foam Process Development: A Systems Engineering Approach," Journal of Applied Polymer Science, Volume 16, Pages 1387-1402 (1972), but is believed by the present inventor to be in error in its assumption that the rate of evaporation as obtained from the heat balance could be converted directly into a rate of volume expansion which assumes uniform pressure distribution. This approach disregards the stress factor.
There remains, therefore, a very real and substantial need for a viscometer which will simply and economically provide accurate, small-scale results which are adapted to be used on a large-scale basis or, in the alternative, provide direct large-scale results, if desired.